Vehicles with heat engines are nowadays equipped with exhaust lines that include pollution control members such as catalytic purification members and/or particle filters. In order to permit satisfactory operation of such pollution control members it is necessary for the exhaust gases to reach them at a high temperature. It is therefore expedient to avoid too great a loss of heat in the exhaust line and especially in the manifold separating the outlet of the heat engine from the first pollution control member.
Various solutions have been envisaged to that end. In particular, manifolds comprising internal ducts maintained in an outer shell separated from the internal ducts by an air space or an insulating material are found to be effective in avoiding too great a loss of heat.
Such manifolds comprise a flange for fixing to the cylinder head of the engine, on which there come to bear on the one hand the internal ducts and on the other hand the outer shell. An outlet flange is also fixed to the outer shell, allowing the remainder of the exhaust line, and especially the turbocompressor, to be assembled.
Tightness for that type of assembly is ensured by the tight welding of the outer shell to the cylinder-head flange and the outlet flange.
The object of the invention is additionally to achieve satisfactory tightness between the internal ducts and the flanges, especially the outlet flange.
Such tightness is necessary when a material is used between the internal ducts and the outer shell, especially in the case of insulating materials or holding elements based on ceramics fibres, in order to prevent all or some of the material from being sucked in either by the engine or by the exhaust line, and especially the turbocompressor.
Connection and tightness between the internal ducts and the flanges are tricky to achieve because of the differential expansions, especially axial expansions, that are noted between the internal ducts and the outer shell. It is in fact impossible to connect the outer shell and the internal ducts rigidly to the cylinder-head and outlet flanges.
The object of the invention is to propose an exhaust manifold having a satisfactory connection and satisfactory tightness between the internal ducts and the outlet flange.
Tightness in the region of the cylinder-head flange is in that case assumed to be satisfactory and the connection with the flange is considered to be rigid.
The invention therefore proposes to achieve satisfactory tightness on the outlet flange side without imposing a rigid connection between the internal ducts and that flange.